Solid-state light sources for curing and surface modification

ABSTRACT

The systems and methods described herein relate to solid-state light sources capable of generating radiation beams for, but not limited to, the treatment of surfaces, bulk materials, films, and coatings. The solid-state ultraviolet source optically combines the light output of at least two and preferably as many four independently controllable discrete solid-state light emitters to produce a light beam that has a controllable multi-wavelength spectrum over a wide range of wavelengths (i.e. deep UV to near-IR). Specific features of this light source permit changes in the spectral, spatial and temporal distribution of light for use in curing, surface modification and other applications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an apparatus and method of providingsubstantially improved radiation beams for the treatment of surfaces,thin films, coatings, fluids or objects. More particularly, the presentinvention pertains to an apparatus and method for optically combiningthe light output of at least two arrays of solid-state light emitters toproduce a light beam that has a selected spectrum chosen forapplications requiring a wide range of wavelengths to improve oraccelerate a treatment process with a controllable irradiance.

2. Description of the Prior Art

Radiant energy is used in a variety of manufacturing processes to treatsurfaces, films, coatings, over layers, and bulk materials. Specificprocesses include but are not limited to curing, fixing, polymerization,oxidation, purification, or disinfections. By way of example, themanufacture of components for motor vehicles involves the application ofunder coatings, paints or clear coatings on vehicle surfaces for variouspurposes including corrosion resistance, decoration or surfaceprotection (e.g. scratch resistance). The coatings or paints are resinsor polymer-based materials that are applied as liquids or powders andrequire thermal or radiant energy processing to become solids. Theprocessing of coatings or paints by thermal methods is slow and requirestimes ranging from minutes to hours to complete. In addition, somematerials (for example, substrates or coating components) may be heatsensitive and damaged by thermal treatments.

Non-thermal curing using radiant energy to polymerize or effect adesired chemical change is rapid in comparison to thermal treatment.Radiation curing can also be localized in the sense that curing canpreferentially take place where the radiation is applied. Curing canalso be localized within the coating or thin film to interfacial regionsor in the bulk of the coating or thin film. Control of the curingprocess is achieved through selection of the radiation source type,physical properties (for example, spectral characteristics), temporalvariation, or the curing chemistry (for example, coating composition).

A variety of radiation sources are used for curing, fixing,polymerization, oxidation, purification, or disinfections of a varietyof targets. Examples of such sources include but are not limited tophoton, electron or ion beam sources. Typical photon beam sourcesinclude but are not limited to arc lamps, incandescent lamps,electrodeless lamps and a variety of electronic (that is lasers) andsolid-state sources (that is solid state lasers, light-emitting diodesand diode lasers). Selection of a specific radiation source for anapplication is contingent on the requirements of the treatment processand the characteristics of the radiation source. These characteristicsare related to but are not limited to the physical properties of thesource, its efficiency, economics, or characteristics of the treatmentprocess or target. For example, arc lamps or radio-frequency ormicrowave driven “electrodeless” ultra-violet sources efficientlyproduce high levels of radiated power having applications in many“industrial” processes where rapid treatment using significant levels ofirradiance or energy density over large areas are needed. Arc orelectrodeless lamps require high voltage, microwave or radio frequencypower supplies and in the case of microwave-driven systems, a microwavetube (that is a magnetron). These high-powered lamps also requirecooling and heat rejection systems. Such operational requirements limitthe application of such photon sources to situations were this need canbe met.

The spectral emissions of arc and electrodeless lamps are controlled bythe conditions under which the lamp is operated, the particular gasesused to fill the bulb and the selection of various additives placed inthe bulb. Those skilled-in-the-art formulate specific lamp fills meetingcuring needs for many photochemical processes, but gaps exist inspectral coverage in certain spectral ranges.

Solid-state light sources, such as, but not limited to, light emittingdiodes (LEDs), diode lasers, diode pumped lasers and flash lamp-pumpedsolid-state lasers provide emission sources that can tuned to the neededwavelength or can be combined as arrays to provide a multi-wavelengthsource for applications needing broadband source. Advances insolid-state source technology provide high-brightness ultraviolet LEDssuitable as sources for radiation treatment.

At the present time, commercial UV emitting diodes emitting radiationdown to an output of 370 nm. are available from Nichia, Cree, Agilent,Toyoda Gosei, Toshiba, Lumileds and Uniroyal Optoelectonics (Norlux).

UV emitting LEDs and laser diodes are constructed using large band gaphost materials. InGaN based materials can be used in LEDs emitting atpeak wavelengths ranging from 370 to 520 nm (for example, from theultraviolet (UV-A) to visible green). The band gap of GaN is 3.39 eV andcan accommodate luminescent transitions as large as 363 nm. Thesubstitution of In into the GaN host provides localized states that canradiate in the ultraviolet down to 370 nm.

Other nitride materials such as InAlGaN can emit ultraviolet radiationin wavelengths as short as 315 nm. InAlGaN is already being used to makehigh brightness LEDs and laser diodes that operate in the range of 315to 370 nm. Hirayama et. al (Appl. Phys. Lett. 80,207 (2002)) reportsdevices employing layered structures of InxGa1−xN or quaternaryInxAlyGa1−x−yN grown on AlxGa1−xN (x=0.12−0.4) have been used inmultiple quantum well structures to produce sources emitting comparableflux at 330 nm to InGaN devices operating at 415-430 nm. Hirayama et al.(Hirayama et al, Appl. Phys. Lett, 80, 1589 (2002)) has also reported aroom temperature LED source using an improved multiple quantum well(MQW) structure and InAlGaN materials which emits intense UV radiationat 320 nm and significant emission at 300 nm.

Hirayama et al. (Appl. Phys. Lett. 80, 37 (2002)) report thatAlxGa1−xN(AlN)/AlyGa1−yN MQWs exhibit efficient photoluminescencebetween 230 to 280 nm and that the photoluminescence is as high as thatof the InGaN-based materials used in the violet diodes now commerciallyavailable. AlN-based materials are likely candidates for makingultraviolet LEDs operating in the UV-B or UV-C ranges. Other researchersare studying carbide and diamond materials as hosts for deep-UV based onthe fact that their band gaps are as large as AlN.

LEDs operating in the blue, violet and UV-A (390 nm) wavelengths are ofsufficient radiance to be used in ultraviolet and photochemical curingas “spot” curing sources. U.S. Pat. No. 6,331,111B1 (Cao) and EP0-780-104 (Breuer et al) describe hand held portable spot curing lightsystems using solid state light sources consisting of light emittingdiodes or diode laser chips. The light source of Cao may contain sourcesthat emit multiple wavelengths so that numerous components in materialswhose photo initiators are sensitive to different wavelengths may becured at once. In the preferred embodiment described in Cao, the lighttravels directly to the curing surface without going through an opticaldevice like a light guide or optical fiber. Breuer et al. describe asimilar device optimized to cure dental resins and also extend claims toapparatus where the irradiator is a stationary curing apparatus whoselight source chips are fixed to the walls of the curing chamber.

Various light sources have been used for the purposes of curingcomposite materials. These include plasma, halogen, fluorescent, and arclamps. Various lasers have been incorporated in curing apparatus. Lasersemitting ultraviolet beams include frequency doubled or re-doubledsources like the 266 nm Nd-YAG systems, argon-ion systems and Nd-YAGpumped OPOs (optical parametric oscillators). Cao cites U.S. Pat. Nos.5,420,768, 5,395,769, 5,890,794 and 5,161,879 where LEDs have beenemployed as curing light sources. The application of solid state sourcesto the curing process are also described in U.S. Pat. Nos. 6,127,447 and5,169,675.

Technology necessary for the application of solid-state sources in thetreatment process can be found in the development of LED and laser diodeequipped systems for illumination and solid-state displays. Thesesystems include an apparatus for LED illumination that can beincorporated into a hand-held lamp, are battery powered and equippedwith electronics that provide pulsed power to control lamp radiance andcompensate for the decrease in battery voltage during battery discharge.Published U.S. Patent Application 2002/0017844 A1 teaches the use ofoptical systems to modify the field of view for LED emitters in displayswhere the field-of-view is restricted.

There are many examples in the prior art of the use of LEDs in arrays tosynthesize multi wavelength emissions. U.S. Published Patent ApplicationNo. 2001/0032985 A1 teaches the installation of arrays of colored LEDson a chip to make multicolored or white solid-state illuminationsources. U.S. Pat. Nos. 6,016,038 and 6,150,774 disclose the method andelectronics needed to generate complex, predesigned patterns of light inany environment. The use of computer controlled LED arrays to providelight sources capable of rapid changes in illumination and spectralselection are detailed in U.S. Pat. No. 6,211,626, which describes asystem using sub-arrays of primary colored (red, green and blue) LEDswhose individual elements are addressable and which can be controlled bypulse modulation to emit varying amounts of light to synthesize a thirdcolor. U.S. Pat. No. 6,211,626 indicates that such computer-controlledarrays of light emitters are not new but that previous systems hadlimitations, which reduced the flexibility or efficiency of theillumination system. The use of computer control for lighting networksused in illumination is described in U.S. Pat. Nos. 5,420,482, 4,845,481and 5,184,114.

U.S. Published Patent Application No 2002/0191394 teaches the use of adiffractive optical element (diffraction grating) for mixing light frommonochromatic light sources like LEDs and making multicolor or whitebeams. The monochromatic light sources are positioned relative to thegrating where light of that frequency is found in the diffracted orderbeams higher than the zeroth order. The mixed beam is the zeroth orderbeam. A white beam will be provided if sufficient frequencies arerepresented in the first and higher order beams being directed on thegrating. Fraunhoffer diffraction is used to mix the monochromatic beams.This is different from the use of Fresnel Zone plates to accomplish thecoupling of the multiple radiation sources

SUMMARY OF THE INVENTION

The present invention provides a solid-state light source and methodwhich optically combines (mixes) the light output of at least two andpreferably additional independently controllable discrete solid-statelight emitter arrays to produce a light beam that has a selectedmulti-wavelength spectrum over a wide range of wavelengths such as fromdeep UV to near-IR to provide irradiance of a target surface with acontrolled power level. Optical mixers combine light spectrums which areprovided from the light emitter arrays to produce the controllablemulti-wavelength spectrum.

Specific features of this light source permit changes in the spectral,spatial and temporal distribution of light for use in curing, surfacemodification and other applications.

This light source can be adjusted to precisely match the physicalcharacteristics of the applied light to the chemical properties ofmaterials to provide a means to improve the process at both nanometerand greater length scales by:

-   -   (1) optimizing the degree and rate of cross-linking of polymeric        materials;    -   (2) selecting specific cross-link bonding in polymers;    -   (3) matching light source characteristics to specific        photo-initiators;    -   (4) controlling the distribution, penetration or rate of light        energy deposition in materials to create new morphologies; and    -   (5) optimizing light source characteristics for surface        processing.

A preferred embodiment of the invention comprises at least two solidstate light emitting arrays which preferably are LED arrays, each ofwhich has a characteristic emitting frequency (wavelength), an opticalmixer to mix the radiation from the LED arrays, a reflector toconcentrate radiation from the arrays and to provide a two-dimensionalenergy distribution on the target surface to be treated which isoptionally substantially uniform. An optional cooling system may beprovided to provide high stability of the spectral output and to improvelifetime of arrays.

The invention increases the flexibility of the photochemical processes(especially, but not limited to, UV-curing of inks and the like,plastic, thermal paper, liquid crystal and the like) by eitheroptimizing existing ultraviolet treatment processes and outcomes, orcreating entirely new treatment processes or outcomes. The inventionperforms these tasks by providing a light source whose spectralemissions can be varied to provide changes in the ultraviolet light suchas to changes in the brightness, chromaticity, colorimetric purity, hue,saturation and lightness of visible light. Modification of physicalcharacteristics of light provides configuration of a light source tomake the best use of the physical and chemical properties of curablematerials.

Other problems which the invention overcomes include curing applicationswhere the use of technology normally included in light sources cannot beused for technical, process or economic reasons. This includes but isnot limited to:

(1) high voltage cabling, electronics and power supplies;(2) RF or microwave cabling, wave guides, electronics and powersupplies;(3) gaseous electronic components including electrode and electrode-lessbulbs(4) high power electronics and the needed heat dissipation systems.

The invention also provides a solution to the problem of unwanted lightemissions such as infrared from curing sources. Ultra-violet solid-statelight emitter arrays generate little or no emissions in the infrared. Ifinfrared radiation is needed in the curing process, infrared emitters ofthe desired wavelength and energy can be configured into the solid stateUV generating arrays providing the selected wavelengths which areincluded in the curing light system to provide the desired missedspectrum.

The frequency spectrum of the individual light emitting arrays is choseneither (1) to provide a composite frequency made up of the mixedspectrum from the individual arrays required for the desiredapplication, or (2) each array provides the identical common frequencyspectrum to increase the power level of irradiance of the commonfrequency spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side elevational view of a first embodiment of the presentinvention; FIG. 1B is a perspective view of the first embodiment of thepresent invention; and FIG. 1C is an example of a light emitting arraywhich may be used with the practice of the various embodiments of theinvention.

FIG. 2 is the spectral distribution of irradiance of one of the LEDarrays in FIG. 1 showing ultraviolet radiation source emission near 390nanometers.

FIG. 3 is a spectral distribution of irradiance of the other LED arrayin FIG. 1 showing an ultraviolet radiation emission near 410 nanometers.

FIG. 4 is a spectral distribution of irradiance produced by opticalmixing of the individual spectral radiance distribution of the LEDarrays of the embodiment of FIG. 1 with the spectrums illustrated inFIGS. 2 and 3.

FIG. 5 is a spectral distribution of irradiance of the individual LEDarrays showing the individual components of FIGS. 2 and 3 and theoptical mixing thereof as illustrated in FIG. 4.

FIG. 6 is a comparison between measured and simulated spectralirradiance showing simulated spectral irradiance as a line and ameasured spectral irradiance as diamonds regarding the embodiment ofFIG. 1.

FIG. 7 is a spectral distribution of irradiance of the embodiment ofFIG. 1 operated with the 390 nm LED array operated with a bias voltageof 47 volts and the 405 nm LED array operated at a bias voltage 0, 34,35, and 38 volts respectively.

FIG. 8 shows an embodiment of the invention using two solid state lightemitting arrays as illustrated in FIG. 1, including a housing with aninterior elliptical reflector installed in a lamp enclosure providingcooling to the solid state light emitting arrays and a controller forcontrolling the power and spectral output produced by the individualsolid state light emitting arrays.

FIG. 9 is a perspective view of a second embodiment of the inventionutilizing three solid state light emitting arrays, three semitransparentmirrors functioning as optical mixers and an interior cylindricalreflector.

FIGS. 10A and 10B show a simulated flux distribution of the secondembodiment of FIG. 9.

FIG. 11 illustrates a perspective view of a third embodiment of theinvention in which four solid state light emitting arrays are placedbetween four semitransparent mirrors functioning as optical mixingelements and an interior cylindrical reflector.

FIG. 12 is a perspective view of a fourth embodiment of the inventionwith four solid state light emitting arrays placed on the edges of fouroptical mixers and a cylindrical interior reflector.

FIG. 13 is a perspective view of a fifth embodiment of the inventionwith six solid state light emitting arrays placed between six opticalmixing elements.

FIG. 14 is a perspective view of a sixth embodiment of the inventionwith six solid state light emitting arrays placed on edges of sixoptical mixing elements.

FIG. 15 is a perspective view of an seventh embodiment of the inventionwith six solid state light emitting arrays arranged facing eight opticalmixers arranged in an octahedron.

FIG. 16 is a perspective view of an eighth embodiment of the inventionwith six solid state light emitting arrays facing eight optical mixers.

FIG. 17 is a perspective view of a ninth embodiment of the invention ofeight solid state light emitting arrays facing four optical mixersarranged to face a structure with tetrahedral symmetry.

FIG. 18 is a perspective view of an tenth embodiment of the inventionwith four solid state light emitting arrays spaced between fourintersecting optical mixing elements contained in an internalellipsoidal reflector.

FIG. 19 shows the flux distribution of the ninth embodiment of FIG. 18.

FIG. 20 is a perspective view of an eleventh embodiment of the inventionwith two elongated solid state light emitting arrays facing an opticalmixer contained in an internally reflective elliptical reflector.

FIG. 21 is a perspective view of a twelfth embodiment of the inventionwith two elongated solid state light emitting arrays facing a prismaticmixing device contained in an elliptical reflector.

FIG. 22 is a perspective view of a thirteenth embodiment of theinvention with two elongated solid state light emitting arrays facingone optical mixing element contained in a reflector with an ellipticalcross section.

Like reference numerals identify like parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a solid state light source and a method ofirradiating a target surface with a solid state light source whichutilizes solid state light emitting arrays each preferably comprising aplurality of light emitting diodes (LEDs) which are mounted on a flatsurface. Each diode emits light away from one side of the flat surfacetoward a target surface with at least one wavelength which is chosen tosatisfy the desired application. At least one optical mixer is providedwith each mixer mixing the output of a pair of solid state lightemitting arrays. Each optical mixer is positioned symmetrically withrespect to a pair of light emitting solid state arrays. Each opticalmixer reflects part of the light output from a symmetrically disposeddiode array and transmits part of the light output from anothersymmetrically disposed light array to provide a composite mixed lightspectrum to irradiate the target surface with mixed light which has aselected frequency spectrum with the irradiance level of the spectrumbeing controllable by a variable control parameter such as voltage, butit should be understood that the invention is not limited thereto. Theat least one optical mixer may be designed to substantially split(50-50) the light incident thereon from each array into a part which isreflected and a part which is transmitted through the optical mixer.With respect to the portion of the light which is transmitted throughthe optical mixer from the first light emitting array, the lightincident on an opposite surface of the optical mixer from the otherlight emitting array which is reflected is optically mixed with theportion transmitted through the optical mixer from the first lightemitting array. A composite wave front comprised of the mixed componentsof light from each of the symmetrically disposed solid state lightemitting arrays is transmitted toward the irradiated target surface. Asis described below, a controller controls the power applied to the lightemitting arrays to control the irradiance which is incident on thetarget surface. Each light emitting array may have a substantiallysimilar frequency spectrum or have a different frequency spectrum.

When the frequency spectrums of the symmetrically disposed lightemitting arrays are different, the overall frequency of the irradianceon the target surface is a summation of the individual frequencyspectrum output by the individual light emitting arrays. In each of theembodiments of the invention, mixing is produced by one or more opticalmixers which may be a partially reflective and partially transmissivemirrors which may transmit and reflect substantially equal parts ortransmit and reflect unequal parts or a prism which is irradiated by thelight from the individual solid state light arrays to provide mixingthereof.

FIGS. 1A and 1B illustrate a first embodiment 10 of the presentinvention. FIG. 1A is an elevational view with a section taken through acurved internally reflective housing 21; FIG. 1B is a perspective viewof the embodiment 10; and FIG. 1C is an illustration of a suitable lightemitting array which may be used with the practice of the invention.

The first embodiment 10 is illustrative of a basic solid state lightsource in accordance with the present invention. Each of light emittingarrays 12A and 12B may be manufactured in accordance with any well-knowntechnique. The surface 14 of each of the pair of symmetrically disposedsolid state light emitting arrays which, in a preferred embodiment, areLEDs output light rays 16 which pass directly to the target surface 18.Other light rays 17 produce a combined irradiance produced by opticalmixing element 20 on which the rays 17 are incident thereon. As may beseen in FIG. 1A, the interior of housing 21 has an internally reflectivesurface 22 which functions to reflect any light output from either ofthe light emitting arrays 12A or 12B toward the target surface 18 toprovide controlled irradiance which, in a preferred embodiment, ispreferably substantially uniform thereon as described below inconjunction with FIGS. 2-6 in view of the curvature of surface 22 beingelliptical with the optical mixer being near the focal axis of theelliptical curvature. Light rays 16, 17 and 19, which are output fromthe light emitting arrays 12A and 12B and do not pass through theoptical mixer 20, are shown as solid lines and light rays 22 passingthrough the optical mixer 20, from either of the light emitting arrays12A or 12B are shown as dotted rays. Parallel solid line rays 19 anddotted rays 22 symbolize the net mixing performed by the optical mixer20 for the rays emitted from the surfaces of the light emitting arrays12A and 12B which partially transmits and partially reflects the lightemitted from the pair of light emitting arrays. The degree of reflectionand transmission may be varied from an equal splitting.

The housing 21, while preferably having an elliptical cross section, mayutilize other curved cross sections which facilitates convergingdivergent light rays produced by the solid state light arrays 12A and12B being directed toward the target surface 18 as indicated by arrows24.

The pair of light emitting arrays 12A and 12B are illustrated as squareflat panels. The light emitting arrays are comprised of a plurality ofdevices, such as LEDs, which emit radiation in the ultraviolet range butthe invention is not limited thereto with a suitable construction beingdescribed below in conjunction with FIG. 1C. For example, in a highpower irradiation apparatus in accordance with the embodiment 10 ofFIGS. 1A and 1B, the arrays 12A and 12B may respectively be an array of40 LEDs as described in FIG. 1C which individually emit at 400 mW at 405nm mounted on an integrated circuit of approximately 1 square cm. Theother radiation source 12B may, without limitation, be an array of 40LEDs as described below emitting 100 mW at 390 nm mounted on anintegrated circuit of approximately 1 square cm. Additionally, theoptical mixing element 20 may be semi-reflective mirror whichsubstantially equally splits the emission from the rays 16 intoreflected rays 19 and transmitted rays 22 which are mixed as indicatedby the aforementioned parallel solid and dotted lines 19 and 22 suchthat the rays are superimposed onto each other. A semi-reflectivemirror, which may be utilized as the optical mixer 20, may be a UVtransmitting quartz plate that is coated with a thin chromium film thatreflects and transmits approximately 50% of the incident light. Thelight emitting diode arrays 12A and 12B are symmetrically positionedwith respect to the optical mixer 20 such that virtual images ofradiation sources are superimposed to create in a preferred embodiment amixed light source comprising substantially equal amounts of light fromeach of the light emitting arrays.

FIG. 1C illustrates a suitable construction for the light emitting solidstate arrays 12A and 12B with a scale of approximately 5:1 for the firstembodiment as described above and in the embodiments as described below.The array 60 is comprised of 40 LEDs 62. A lower bus bar 64 has a groupof 8 LEDs mounted thereon. Each of the LEDs 62 mounted on the lower busbar 64 are in turn coupled by a wire 66 by means of wire bonds 68 whichconnect the wire extending from the individual LEDs to four upper busbars 64 on which 4 LEDs are mounted. A lens 70 focuses light emitted bythe individual LEDs 62 toward the optical mixer 20. A thermal sensor 72is utilized to provide temperature control for the LED array 60. The LEDarray 60 is mounted on a hexagonal substrate 74. Electrical terminals 76are mounted on the hexagonal substrate 74 to provide suitable electricalcontacts for electrical power of the array.

The light source represented by the light emitting solid state arrays12A and 12B and the optical mixer 20 is positioned approximately at thefocus of the elliptical reflector 22 which is preferably substantiallyone-half of an ellipse. However, the reflector 22 may be more or lessthan one-half of an ellipse if desired and may be a non-ellipticalsurface. Since the reflector 22 is part of an ellipse, the reflector 22has a major axis, a minor axis, a first focal axis within the reflector,and a second focal axis outside the reflector. The light sourcecomprised of the aforementioned light emitting and optical mixer ispreferably positioned on the first focal axis. Light beams from thearrays of diodes 12A and 12B are transmitted and reflected by theoptical mixer 20 and strike the elliptical reflector 22 that directs thelight beams to the second focal axis of the elliptical reflector 22proximate to the target surface 18. The target surface 18 is placedsubstantially at the second focal axis where the light beams aredirected to strike the irradiated surface thereof. The location of thetarget surface 18 at the second focal axis maximizes the irradiance atthe second focal axis. The irradiated surface 60 can also be placedbeyond the second focal axis such as at the far field to increase thearea which is irradiated.

FIGS. 2-6 illustrate the optical performance of the radiation on thetarget surface 18 using the first embodiment 10. The spectral readingswere obtained using an integrated sphere and a spectral radiometer(Ocean Optics model S2000) based on techniques well-known in the fieldof illumination. The radiation sources were 40 light emitting diodeswhich are high flux density solid state modules manufactured by NorluxMonochromatic Hex (NHX) emitting either ultraviolet UV-A at a peakemission at 390 nm or ultraviolet UV-B at 405 nm with a peak emission at410 nm. The LED arrays 12A and 12B were independently connected to DCpower supplies operated at a constant voltage mode. A forward biasvoltage turned the diodes on to produce the UV spectra of FIGS. 2-6.

FIGS. 2 and 3 show the spectral irradiance of the source 12A which is aUV-A emitter and the source 12B which is a UV-B emitter. Radiationsource 12A was operated at forward bias of 15.6 volts and a current of200 nA. Array 12A emitted UV-A ultra-violet radiation that peaked at 395nm and extended from 385 to 405 nm (Full-Width-at-Half-Maximum) (FWHM).Diode array 12B was operated at a forward bias of 19 volts and a currentof 200 mA to produce UV-B ultraviolet radiation that peaked at 410 nmand extended from 400 to 418 nm (FWHM).

FIG. 4 shows a measured spectral radiance of embodiment 10 when bothradiation sources 12A and 12B were operated simultaneously. Thecomposite spectrum peaked at 410 nm and extends from 392 to 418 nm FWHM.The LED array 12A was operated at 15.6 volt forward bias, whereas theLED array 12B was operated at 17.5 volts forward bias. The spectrum is acomposite of the summed emission from the two LED arrays 12A and 12B.

FIG. 5 illustrates the simulated spectrum produced by the summation ofthe individual emission spectra of the diode arrays 12A and 12Billustrated in FIGS. 2 and 3.

FIG. 6 is a comparison of the simulated and measured spectra of theembodiment 10. The measured spectra are identified by diamonds andsimulated spectra are identified by lines. The measured spectrum matcheda simulated spectrum over the entire range of emission from the lightemitting arrays 12A and 12B and shows an excellent mixing of the beamsfrom the two radiation sources.

The power levels of the light from the light emitting arrays 12A and 12Bare controlled by varying the electrical bias applied thereto whichchanges the forward bias current of the diodes. The variation of voltageor another electrical parameter of the individual light emitting arrays12A and 12B permits the variation of the spectral characteristic of themixed light by choosing the magnitude and frequency of the spectra thatare mixed by the optical mixer 20.

FIG. 7 shows how the spectral composition of a beam from the embodiment10 can be changed continuously from (1) a spectrum 90 representing thewavelengths from the diode array 12A, (2) a spectrum 92 with equivalentcontributions from the diode arrays 12A and 12B, (3) a spectrum 94 withan increased spectrum from the array 12B, and (4) finally to a spectrum96 with the dominant contribution from the array 12B. This demonstratesan important function of the embodiments of the invention including therepresentation of the spectral composition of FIG. 1 which permitsgeneration of a spectrum with variable ultraviolet spectral weight.

FIG. 8 illustrates a system 120 incorporating the embodiment 10 of FIG.1 into a lamp housing 130 which is equipped with a cooling system forthe LED arrays 12A and 12B. The air cooling system may be by forced airutilizing one or more fans inducting air into the housing and blown pastthe interior curved reflector 21. As may be seen, pathways exist for theingress and egress of cooling air. A controller 170 is coupled viaconnection 172 to the solid state light source. The curved reflector 21is mounted in the lamp housing 130 with the reflector being attached toa base of the lamp enclosure that has a rectangular opening 180 fromwhich light rays 182 pass to the target surface 18. The LED arrays 12Aand 12B are air cooled by two fans 162 which push air into the lampenclosure 130. A slot 190 is cut into the curved reflective surface 21to permit air to be pushed into the lamp enclosure 192 to allow the airto impinge on heat sinks 194 of the LED arrays 12A and 12B which areattached thereto. The fans 162 may be powered from a 12 volt powersupply. The LED arrays 12A and 12B will suffer a loss of light emittingpower if a surface temperature of the substrate to which the LEDs 12Aand 12B are attached exceeds 40° C. with current commercially availableproducts. The power to the diode arrays 12A and 12B and the speed of thefans 162 is adjusted to keep the LED chip surfaces below the maximumtemperature, such as 40° C. The controller 170 may be digitallycontrolled which permits programming of the voltage to be applied toeach of the diode arrays 12A and 12B in order to produce a variation inthe summed output radiation as reflected, for example by the curves90-96 in FIG. 7 once the frequency spectra is determined by the choiceof the individual solid state light emitting elements of the array.

FIG. 9 illustrates a third embodiment 230 of a solid state light sourcein accordance with the invention which is comprised of three LED arrays232A, 232B and 232C and three optical mixers 250 which intersect at acentral point 252 within cylindrical reflector 254. The three LED arrays232A, 232B, and 232C produce spectra which are mixed by thesymmetrically disposed optical mixer 250 located therebetween. Theaforementioned LED arrays and symmetrically positioned optical mixtures250 perform the same function as described above with respect to thefirst embodiment 10 of FIG. 1. The individual optical mixers 250 whichintersect at central point 252 have an occluded angle of 120° betweenthe adjacent optical mixers. The optical mixers 250 preferably aresemi-reflective mirrors which split the emission substantially equallyfrom the LED arrays 232A, 232B and 232C into three transmitted andreflected beams of substantially equal intensity which are superimposedonto each other as indicated in FIG. 1 by the superimposed light rays 19and 22. However, this embodiment may use optical mixers which do nottransmit and reflect equal parts. The three optical mixers 250 aresymmetrical when rotated through an angle of 120°.

FIGS. 10A and 10B show the results of ray tracing simulations to predictthe irradiance distribution 272 in the XZ plane as illustrated in FIGS.10A and 10B for the second embodiment 230. The radiance profiles fortraces parallel and perpendicular to the X or Z axis through the centerof the irradiance distribution show small asymmetry 272. The asymmetryis a consequence of a lack of symmetry of the embodiment 230 torotations 900 along an axis perpendicular to the XZ plane through thecenter of the embodiment 230.

FIGS. 11 and 12 respectively show a third and fourth embodiment 360 and400. The designs respectively differ in the placement of the four LEDarrays 232A-232D arrays relative to the intersection 362 of theplacement of the optical mixers 350 so that the diode arrays 332A-332Dare positioned between the edges 352 in FIG. 11 and face the edges 350in FIG. 12. In the third embodiment 340, the LED arrays 332A-332D facethe point of intersection 362 while in the fourth embodiment 370, thelight emitting arrays 332A-332D face the edges 352 of the optical mixers350. In the third and fourth embodiments, a cylindrical internallyreflective housing 360 contains the LED arrays 332A-332D and the fouroptical mixers 350 centrally disposed relative thereto which are joinedtogether at central location 362 to form a cross. In the fourthembodiment 370 a solid line indicates light rays which are visible tothe viewer and a dotted line indicates rays which are occluded fromdirect view. It should be understood that the connections to a suitablecontroller and cooling system for the light emitting arrays, such asillustrated in FIG. 8, are not illustrated for purposes of simplifyingthe illustration.

FIGS. 13 and 14 show fifth and sixth embodiments 400 and 420respectively of the invention which have been simplified to only showthe LED arrays emitted. The internally reflective curved housing hasbeen omitted along with the controller of the individual LED arrayswhich is used to produce a controlled application of power to theindividual LED arrays to produce a variable spectrum as discussed above.The embodiment 400 of FIG. 13 has three pairs of LED arrays 432A and432B which are symmetrically disposed relative to optical mixers 440.Pairs of LED arrays 432A and 432B work in concert with their centrallydisclosed optical mixer 440 to provide the same function as describedabove with respect to the first embodiment 10 to produce a controlledmixing of the light emitted from the surface of the pairs of the LEDarrays. The difference between the embodiments 400 and 420 resides inthe respective placement of the pairs of LED arrays 432A and 432Brelative to the optical mixers 440. In the embodiment of 400, the pairs432A and 432B face the point of intersection 442 of the optical mixers440 and in the embodiment 420, the pairs 432A and 432B face the edges444 of the optical mixers 440. The six optical mixers 440 are joinedtogether at a central location 442 which is centrally disposed relativeto the faces of the LED arrays 432A and 432B. The light from the threepairs of LED arrays 432A and 432B are combined by transmission andreflection of the six optical mixers 440 in accordance with theprincipal operation described above. While not illustrated, theembodiments 400 and 420 of FIGS. 13 and 14 may be placed inside of acylindrical internally reflective housing of the type illustrated inFIGS. 1, 9, 10 and 11 so as to cause light to be transmitted toward atarget surface 18. Additionally, a controller and a cooling system, suchas that described above with respect to FIG. 8, may be utilized tocontrol the emission of light from the LED arrays. The six opticalmixers 440 in the embodiments 400 and 420 form a cross at a point ofintersection 442 and preferably have the characteristic of reflectingand transmitting substantially equal intensity light. A solid lineindicates light rays which are visible to the viewer and a dotted lineindicates rays which are occluded from direct view.

FIG. 15 shows a seventh embodiment 500 having three pairs of lightemitting diode arrays 532A and 532B which are symmetrically disposedabout eight optical mixers 550 which are triangular semi-transparentmirrors which function to split the irradiation sources 532A and 532Binto transmitted and reflected beams of substantially equal intensitywhich are superimposed onto each other in accordance with the mixingfunction as described above with respect to the first embodiment ofFIG. 1. The LED arrays 532A and 532B are placed at the vertices placedat the edges of the optical mixers 550. It should be noted that thecurved internally reflective housing, controller and target surface havebeen omitted from the embodiment of FIG. 15. A solid line indicateslight rays which are visible to the viewer and a dotted line indicatesrays which are occluded from direct view.

The eighth embodiment 560 of FIG. 16 utilizes three pairs of LED arrays532A and 532B which are positioned at the vertices of twelve opticalmixers 550 which are partially reflective mirrors. Mixing of light frompairs of LED arrays 532A and 532B occurs in the manner described above.A solid line indicates light rays which are visible to the viewer and adotted line indicates rays which are occluded from direct view.

FIG. 17 illustrates a ninth embodiment 600 having four pairs of LEDarrays 632A and 632B which face four optical mixers 650 configured in astructure with tetrahedral symmetry. It should be understood that theconnections to a suitable controller and cooling system for the LEDarrays, such as illustrated in FIG. 8, are not illustrated for purposesof simplifying the illustration. A solid line indicates light rays whichare Visible to the viewer and a dotted line indicates rays which areoccluded from direct view.

FIG. 18 shows a tenth embodiment 700 of the present invention having aconfiguration of four LED arrays 332A, 332B, 332C and 332D symmetricallydisposed about four optical mixers 350 in a configuration similar toFIG. 11 except that an ellipsoidal reflector 740 is provided as thehousing. The ellipsoid 740 has a major access, which is also the axis ofrotation of the ellipse that sweeps out the surface of the ellipsoid, aminor axis, a first focus within the ellipsoid and a second focusoutside the ellipsoid which are not illustrated. The LED radiationsource is positioned on the major axis of the ellipsoid reflector 740 atthe first focus. Since the irradiation source is extended, the image ofthe irradiation source will not be brought into sharp focus. Asdescribed above with respect to other embodiments, the internallyreflective curved cylindrical housing, controller and cooling systemhave been omitted. A solid line indicates light rays which are visibleto the viewer and a dotted line indicates rays which are occluded fromdirect view.

FIG. 19 shows the simulated irradiance of the embodiment 700 of FIG. 18on the irradiated surface 18. The radiance pattern of the beam shows aring-like pattern near the peak irradiance. This pattern is due to theplacement of the radiation sources 332A-332D in a circle about theoptical mixers 350. As described above with respect to otherembodiments, the internally reflective curved cylindrical housing,controller, cooling system and target surface have been emitted.

FIGS. 20 and 21 show eleventh and twelfth embodiments 800 and 900 of thepresent invention that utilize elongated linear arrays of diodes 12A′and 12B′ with the embodiment 800 having elongated optical mixer 20′which is a semitransparent mirror and the embodiment 900 utilizing anoptical mixer 902 which is a prism for splitting and mixing beams fromthe arrays 12A′ and 12B′ using internal reflection rather thanreflection from a mirror. As described above with respect to otherembodiments, the internally reflective curved cylindrical housing,controller and cooling system have been emitted.

FIG. 22 shows a twelfth embodiment 1000 which is similar to theembodiment 800 of FIG. 20 regarding the configuration of the elongatedlight emitting diode arrays 12A′ and 12B′ and the elongated opticalmixer 20′. The embodiment 1000 differs with regard to the curvedinternally reflective housing 1002 which is an elliptical reflector witha side reflector as an ellipse with semi-major and semi-minor axis beingparallel and perpendicular to the optical mixer 20′ or a prism such as902 used in the embodiment 900 of FIG. 21 and replacement thereof. Theside reflector 1004 is attached to an elliptical plate 1006 to form anelliptical housing. As described above with respect to otherembodiments, the internally reflective curved cylindrical housing,controller, cooling system and target surface have been emitted.

While the invention has been described in terms of its preferredembodiments, it is intended that numerous modifications can be madethereto without departing from the spirit and scope of the invention asdefined in the appended claims. It is intended that all suchmodifications fall within the scope of the appended claims.

1-5. (canceled)
 6. A solid state light source in accordance with claim26 comprising: a pair of side inward-facing reflectors, each of which isjoined to at least one edge of the curved reflector which reflects lighttoward the surface. 7-9. (canceled)
 10. A solid state light source inaccordance with claim 26 wherein: the at least one optical mixercomprises a partially reflective mirror. 11-14. (canceled)
 15. A solidstate light source in accordance with claim 6 wherein: the at least oneoptical mixer comprises a partially reflective mirror. 16-18. (canceled)19. A solid state light source in accordance with claim 10 wherein: thepartially reflective mirror is approximately 50% reflective. 20-24.(canceled)
 25. A solid state light source in accordance with claim 26wherein: the at least one optical mixer comprises a prism.
 26. A solidstate light source comprising: at least two light emitting arrays, eacharray comprising solid state light emitters which are mounted so thateach emitter emits light away from one side of a surface; at least oneoptical mixer, each optical mixer being positioned symmetrically withrespect to at least one pair of the arrays, reflecting part of the lightemitted from one of the at least one pair of symmetrically positionedarrays and transmitting part of the light emitted from another one ofthe at least one pair of symmetrically positioned arrays to mix thelight from the at least one pair of symmetrically positioned arrays toproduce mixed light which irradiates a surface; a housing comprising aninterior curved reflective surface, the housing containing the at leasttwo light emitting arrays and the at least one optical mixer, andincluding an opening from which the mixed light is emitted and theinterior curved reflective surface reflecting at least part of the lightemitted from the one side of the arrays toward the surface; and acontroller, coupled to at least one of the at least two light emittingarrays, which controls a power level of light emitted from the at leastone power-controlled array in at least one frequency band; and whereinthe power level of the light emitted by the at least onepower-controlled array in the at least one frequency band is chosen toprovide a controlled power level of mixed light to irradiate thesurface. 27-36. (canceled)
 37. A method of irradiating a target surfacewith a solid state light source including at least two light emittingarrays, each array comprising solid state light emitters which aremounted so that each emitter emits light away from one side of asurface, at least one optical mixer, each optical mixer being positionedsymmetrically with respect to at least one pair of the arrays,reflecting part of the light emitted from one of the at least one pairof symmetrically positioned arrays and transmitting part of the lightemitted from another one of the at least one pair of symmetricallypositioned arrays to mix the light from the at least one pair ofsymmetrically positioned arrays to produce mixed light, a controllercoupled to at least one of the at least two light emitting arrays whichcontrols a power level of light emitted from the at least onepower-controlled array in at least one frequency band, a housingcomprising an interior curved reflective surface, the housing containingthe light emitting arrays and the at least one optical mixer and anopening from which the mixed light is emitted and the interior curvedreflective surface reflecting at least some of the light emitted fromthe one side of the arrays to the target surface, the method comprising:positioning the target surface to be irradiated with the mixed lightemitted from the opening; and controlling the power level of lightemitted from the at least one power-controlled array in the at least onefrequency band to provide a controlled power level of mixed light toirradiate the target surface. 38-52. (canceled)
 53. A method inaccordance with claim 37 wherein: the housing further comprises a pairof side inward-facing reflectors, each of which is joined to at leastone edge of the curved reflector which reflects light toward thesurface.
 54. A method in accordance with claim 37 wherein: the at leastone optical mixer comprises a partially reflective mirror.
 55. A methodin accordance with claim 53 wherein: the at least one optical mixercomprises a partially reflective mirror.
 56. A method in accordance withclaim 54 wherein: the partially reflective mirror is approximately 50%reflective.
 57. A method in accordance with claim 37 wherein: the atleast one optical mixer comprises a prism.